The present invention relates to a system for identifying the position of a three-dimensional machine in a fixed frame of reference.
The three-dimensional machine concerned can equally well be a measuring machine or a machine for machining, e.g. a multi-spindle milling machine.
In the particular field of motor vehicles, it can be necessary to identify the position of various points of the bodywork of a motor vehicle that has been involved in an accident or that is being assembled, so as to monitor its shape by identifying predetermined points of said bodywork by means of a three-dimensional measuring device associated with a reference structure, commonly referred to as a xe2x80x9cslabxe2x80x9d. It is this operation of putting the vehicle on the slab that makes it possible to decide whether it can be put back on the road, possibly after repairing its deformed portions, or whether it should be scrapped.
In this context, reference can be made to the following documents in the name of the Applicant: FR-A-2 750 546 and FR-A-2 764 992.
Systems have also been proposed for identifying position by using a transmitter module carrying a light beam source mounted on a stand that is capable of pivoting about two distinct non-parallel axes, with angular position sensors associated with the corresponding rotary movement of the source relative to the stand, a plurality of targets being placed around the transmitter module at locations that are defined relative to a fixed frame of reference, said targets being suitable for delivering electrical signals indicating that they are being illuminated by the light beam emitted by the source. One such system is described in documents WO-A-95/06479 and FR-A-2 669 257. Nevertheless, such a system is constraining insofar as it is necessary to fit the premises in which the measuring machine is to be found with a plurality of projecting targets that are distributed over the vertical walls or the ceiling, with position not being identified relative to the horizontal supporting surface.
Techniques are also known for determining the position of an article, either by means of optical devices of the camera or optical fiber type (U.S. Pat. No. 5,506,682) or by means of a vibrating bar (U.S. Pat. No. 4,617,503), and light benches for industrial metrology are also known (DE-A-197 11 361). The technological background is also illustrated by systems for guiding moving transporters by means of tracks or beacons associated with the ground (U.S. Pat. No. 5,280,431 and U.S. Pat. No. 5,219,036).
An object of the invention is to design a position identifying system that can be used equally well with a measuring machine as with a machining machine, and which is both simple and low in cost. In this context, it is recalled that conventional slabs are constituted by massive plates having dimensions of 200 millimeters (mm)xc3x974000 mmxc3x976000 mm, and they are extremely heavy and expensive.
According to the invention, this problem is solved by a system for identifying the position of a three-dimensional measuring or machining machine in a fixed frame of reference, said machine standing on an essentially plane support surface, wherein:
the support surface is fitted with a plurality of interactive integrated bushings, each bushing being fitted with emitter means serving to emit a predetermined code enabling the bushing in question to be identified and to deduce therefrom the coordinates of an associated point of said support surface; and
the three-dimensional machine is fitted with at least one articulated arm terminated by a position sensor, said arm being fitted with receiver means capable of detecting the code emitted by a bushing amongst the plurality of bushings when the associated position sensor is brought into contact therewith.
Thus, it suffices to bring the position sensor into contact with a plurality of interactive bushings directly adjacent to the machine in order to discover easily the coordinates in three dimensions of a plurality of known points of the support surface, thus making it possible to identify the position of the machine in its frame of reference both quickly and accurately.
In a particular embodiment, at least one essentially vertical surface adjacent to the support surface is likewise fitted with a plurality of interactive integrated bushings of the same type as those fitted to said support surface.
The bushings in a given surface can be positioned so as to form at least a portion of a rectangular grid. In this respect, the array of interactive bushings can be disposed in a wide variety of arrangements without it being necessary to use a rectangular grid arrangement as is the case in particular for conventional slabs where the top bearing surface presents orthogonal grooves which cross at identified points.
Preferably, each bushing comprises a housing integrated in a drilling in the associated surface, said housing containing the emitter means and a position-identifying cone whose axis passes through the identified point associated with said surface. Then, in particular, the emitter means of each bushing is constituted by an infrared emitter associated with an electronics card which is housed in the housing of said bushing.
It is also possible to provide for the position-identifying cone to form a portion of a threaded washer which supports the emitter, said washer being positioned in the housing of the bushing in such a manner that the position sensor is centered on the associated point when it is pressed home in said position-identifying cone.
In which case, advantageously, the washer includes a switch associated with the emitter so that said emitter is active only when the position sensor is pressed home against the position-identifying cone.
Also advantageously, the housing of each bushing can be closed by a removable cover which, in the closed position, lies flush with the plane of the associated surface. Thus, the bushings of the plurality of bushings fitted to the associated surface are fully integrated in said surface and do not provide any impediment to being passed over so long as the bushings are not actually in use.
Finally, and preferably, the coordinates of the position-identifying point of each of the bushings in use are entered in association with the corresponding identity code in a common table, preferably in the memory of an associated processing computer.